Vinyl polymers, such as polystyrenes, are a well known class of materials discovered in the laboratory over 100 years ago. They are light weight, easy to mold and able to maintain their dimensions under adverse temperature conditions. Because of their favorable properties, these materials are used in many commercial applications. Such applications include foam insulators, drinking cups and even refrigerator doors.
Commercial methods have been developed which utilize polyfunctional comonomers to crosslink vinyl polymers. The resulting crosslinked products are typically bulk solids, oddly shaped agglomerated polymeric particles or spherical polymeric particles. Often, said crosslinked products find use in applications where increased dimensional stability and modified viscoelastic properties are desired.
It has been of increasing interest to prepare crosslinked spherical polymeric particles that are monodispersed. The monodispersed polymeric particles can function as calibration standards for microscopy and diffusivity measurement techniques as well as carriers for bioactive substances which include pesticides and other theropeutic agents. Further, crosslinked monodispersed polymeric particles mix uniformly in liquids and polymeric matrices and therefore can enhance the flow and dispersion properties of such mixtures. Better flow and dispersion properties favorably affect the processibility and physical and surface appearance properties of mixtures which contain polymeric particles.
The instant invention, therefore, is based on the discovery of a novel process for producing crosslinked spherical monodispersed polymeric particles. Said crosslinked spherical monodispersed polymeric particles are about 1-6 .mu.m in size and they often contain at least about 0.05 to about 10 weight percent but preferably at least about 0.5 to about 3 weight percent (based on total polymerizable vinyl monomer/vinyl polymer) of a polymerizable polyvinyl monomer. It is noted that the crosslinked polymers of the instant invention are often referred to as gels. Additionally, novel embodiments of the instant invention include the use of a specific dispersion polymerization solvent as well as timed and monitored additions of said crosslinking polymerizable polyvinyl monomer.